https://www.mapquestapi.com/sdk/leaflet/v2.2/mq-map.js?key=${KEY} has been down for at least an hour (could have been longer; that was when it was reported to us). I get a 404 with the content "An error occurred. Sorry, the page you are looking for is currently unavailable. Please try again later.".

Am I doing something wrong? Is there anything I can do to get this working? Or any idea when this will be fixed?

The MapQuest APIs experienced an issue due to Verizon DNS failures from 2:18 - 5:54 am ET. The cause is still being investigated and steps to avoid this type of issue will be assessed. The APIs have since recovered. We apologize for the inconvenience.

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